February 1999
Description
The PBL 3771/1 is a switch-mode, constant-current driver IC (chopper) with two
channels, one for each winding of a two-phase stepper motor. The circuit is especially
developed for use in microstepping applications in conjunction with the matching dual
DAC (Digital-to-Analog Converter) PBM 3960. A complete driver system consists of
these two ICs, a few passive components and a microprocessor for generation of the
proper control and data codes required for microstepping.
The PBL 3771/1 contains a clock oscillator, which is common for both driver
channels; a set of comparators and flip-flops implementing the switching control; and
two H-bridges with internal recirculation diodes. Voltage supply requirements are +5 V
for logic and +10 to +45 V for the motor. Maximum output current is 650 mA per
channel.
A special logic function is used to select slow or fast current decay in the output
stage for improved high-speed microstepping.
The close match between the two driver channels guarantees consistent output
current ratios and motor positioning accuracy.
PBL 3771/1
Precision Stepper Motor Driver
Figure 1. Block diagram.
28-pin PLCC package
22-pin plastic DIP package
24-pin SO package
Key Features
Dual chopper driver in a single
package.
650 mA output current per channel.
Close matching between channels for
high microstepping accuracy.
Selectable slow/fast current decay for
improved high-speed microstepping.
Improved low-level linearity.
Specially matched to Dual DAC
PBM 3960.
Selection of packages, 22-pin
"batwing" DIP, 24 pin "batwing" SOIC
or 28-lead PLCC with lead-frame for
heat-sinking through PC board
copper.
RC
PBL 3771/1
V
MM1
V
MM2
M
A1
M
B1
M
B2
M
A2
GND
C
2
V
R2
CD
2
Phase
2
V
CC
C
1
V
R1
CD
1
Phase
1
E
1
E
2
V
CC
S
R
Q
+
+
Logic
S
R
Q
+
+
Logic
+
1
PBL 3771/1
PBL 3771/1
PBL
3771/1
PBL 3771/1
2
Maximum Ratings
Parameter
Pin no. (DIL)
Symbol
Min
Max
Unit
Voltage
Logic supply
11
V
CC
0
7
V
Motor supply
3, 20
V
MM
0
45
V
Logic inputs
7, 8, 15, 16
V
I
-0.3
6
V
Comparator inputs
10, 13
V
C
-0.3
V
CC
V
Reference inputs
9, 14
V
R
-0.3
7.5
V
Current
Motor output current
1, 4, 19, 22
I
M
-700
+700
mA
Logic inputs
7, 8, 15, 16
I
I
-10
mA
Analog inputs
10, 13
I
A
-10
mA
Oscillator charging current
12
I
RC
5
mA
Temperature
Operating junction temperature
T
J
-40
+150
C
Storage temperature**
T
S
-55
+150
C
** Circuit only. The packaging can handle max 60
C
Recommended Operating Conditions
Parameter
Symbol
Min
Typ
Max
Unit
Logic supply voltage
V
CC
4.75
5
5.25
V
Motor supply voltage
V
MM
10
40
V
Motor output current ***
I
M
-650
650
mA
Junction temperature ****
T
J
-20
+125
C
Rise time logic inputs
t
r
2
s
Fall time logic inputs
t
f
2
s
Oscillator timing resistor
R
T
2
15
20
kohms
*** In microstepping mode, "sine/cosine" drive where I
1
= 650 cos(
) and I
2
= 650 sin(
) mA, otherwise 500 mA/channel both
channels fully on.
****See operating temperature chapter.
Figure 2. Definitions of symbols.
Figure 3. Definition of terms.
50 %
V
CH
t
on
t
off
V
E
| V V |
MA
MB
t
d
t
t
f =
s
ton toff
+
D =
t
t
on
off
+
1
t
on
I I
M OL
I
CC
I I I
I IH IL
I
A
3 300 pF
V
CC
I
I
C
A
V
E
V
V
V
MM
C
820 pF
1 kW
R
S
R
T
T
C
C
R
C
15 kW
I MM
I
RC
RC
PBL 3771/1
20
12
11
V
MM1
V
MM2
M
A1
M
B1
M
B2
M
A2
GND
C
2
V
R2
CD
2
Phase
2
V
CC
C
1
V
R1
CD
1
Phase
1
E
1
E
2
V
CC
22
19
16
13
S
R
Q
15
14
5, 6, 17, 18
+
+
Logic
21
S
R
Q
+
+
Logic
+
3
1
4
2
10
9
8
7
V
V
V
I
IH
IL
V
V
A
R
V
V
CH
C
M
MA
Pin numbers refer to
DIL-package
PBL 3771/1
3
Electrical Characteristics
Electrical characteristics over recommended operating conditions, unless otherwise noted. -20
C - T
J
- +125
C.
Ref.
Parameter
Symbol fig.
Conditions
Min
Typ
Max
Unit
General
Supply current
I
CC
38
50
mA
Total power dissipation
P
D
V
MM
= 40 V, I
M1
= 450 mA, I
M2
= 0 mA.
1.4
1.6
W
Notes 2, 3.
V
MM
= 40 V, I
M1
= I
M2
= 318 mA.
1.6
1.8
W
Notes 2, 3.
Turn-off delay
t
d
3
T
a
= +25
C, dV
C
/dt
50 mV/
s.
1.0
1.5
s
Note 3.
Logic Inputs
Logic HIGH input voltage
V
IH
2.0
V
Logic LOW input voltage
V
IL
0.8
V
Logic HIGH input current
I
IH
V
I
= 2.4 V
20
A
Logic LOW input current
I
IL
V
I
= 0.4 V
-0.4
mA
Reference Inputs
Input resistance
R
R
T
a
= +25
C
5
kohms
Input current
I
R
T
a
= +25
C, V
R
= 2.5 V.
0.5
1.0
mA
Turn-off voltage
V
TO
20
29
38
mV
Comparator Inputs
Threshold voltage
V
CH
R
C
= 1 kohms, V
R
= 2.5 V
430
450
470
mV
| V
CH1
- V
CH2
| mismatch
V
CH,diff
R
C
= 1 kohms
1
mV
Input current
I
C
-10
1
A
Motor Outputs
Lower transistor saturation voltage
I
M
= 500 mA
1.00
1.20
V
Lower transistor leakage current
V
MM
= 41 V, V
E
= V
R
= 0 V, V
C
= V
CC
300
A
Lower diode forward voltage drop
I
M
= 500 mA
1.10
1.25
V
Upper transistor saturation voltage
I
M
= 500 mA
1.20
1.35
V
Upper transistor leakage current
V
MM
= 41 V, V
E
= V
R
= 0 V, V
C
= V
CC
300
A
Upper diode forward voltage drop
I
M
= 500 mA
1.00
1.25
V
Chopper Oscillator
Chopping frequency
f
s
3
C
T
= 3300 pF, R
T
= 15 kohms
25.0
26.5
28.0
kHz
Thermal Characteristics
Ref.
Parameter
Symbol fig.
Conditions
Min
Typ
Max
Unit
Thermal resistance
Rth
J-BW
13 DIL package.
11
C/W
Rth
J-A
13 DIL package. Note 2.
40
C/W
Rth
J-BW
13 PLCC package.
9
C/W
Rth
J-A
13 PLCC package. Note 2.
35
C/W
Rth
J-BW
13 SO package.
13
C/W
Rth
J-A
13 SO package. Note 2.
42
C/W
Notes
1.
All voltages are with respect to ground. Currents are positive into, negative out of specified terminal.
2.
All ground pins soldered onto a 20 cm
2
PCB copper area with free air convection.
3.
Not covered by final test program.
4.
Switching duty cycle D = 30%, f
S
= 26.5 kHz.
PBL 3771/1
4
C
MM2
E
B2
B1
GND
MM1
C
RC
V
M
GND
GND
GND
GND
Phase
CD
A1
GND
GND
GND
GND
GND
1
5
6
7
8
9
10
11
25
24
23
22
21
20
19
4
3
2
1
28
27
26
12
13
14
15
16
17
18
V
R2
V
R1
CD
1
CC
2
2
A2
V
M
M
V
M
Phase
2
1
2
E
1
PBL 3771/1QN
1
2
3
4
5
6
7
8
9
10
11
22
21
20
19
18
17
16
15
14
13
12
B1
E
MM1
A1
GND
GND
1
1
R1
C
CC
M
V
M
GND
GND
Phase
CD
V
RC
M
V
M
Phase
CD
V
V
R2
2
2
A2
MM2
B2
1
E
2
1
C
2
PBL
3771/1N
Figure 4. Pin configuration.
Pin Description
Refer to figure 4.
SO
DIP
PLCC
Symbol
Description
2
1
8
M
B1
Motor output B, channel 1. Motor current flows from M
A1
to M
B1
when Phase
1
is HIGH.
3
2
10
E
1
Common emitter, channel 1. This pin connects to a sensing resistor to ground.
4
3
11
V
MM1
Motor supply voltage, channel 1, 10 to 40 V. V
MM1
and V
MM2
should be connected together.
5
4
12
M
A1
Motor output A, channel 1. Motor current flows from M
A1
to M
B1
when Phase
1
is HIGH.
6,7,
5,6,
1-3,9,
GND
Ground and negative supply. Note: these pins are used thermally for heat-sinking.
18,19
17,18
13-17,28
Make sure that all ground pins are soldered onto a suitably large copper ground
plane for efficient heat sinking.
8
7
18
Phase
1
Controls the direction of motor current at outputs M
A1
and M
B1
. Motor current flows from M
A1
to M
B1
when Phase
1
is HIGH.
9
8
19
CD
1
Current decay control, channel 1. A logic HIGH on this input results in
slow current decay,
a LOW results in
fast current decay, see "Functional Description."
10
9
20
V
R1
Reference voltage, channel 1. Controls the threshold voltage for the comparator and hence
the output current. Input resistance is typically 2.5 kohms,
20%.
11
10
21
C
1
Comparator input channel 1. This input senses the instantaneous voltage across the
sensing resistor, filtered by an RC network. The threshold voltage for the comparator is
(0.450 / 2.5) V
R1
, i.e. 450 mV at V
R1
= 2.5 V.
12
11
22
V
CC
Logic voltage supply, nominally +5 V.
13
12
23
RC
Clock oscillator RC pin. Connect a 15 kohm resistor to V
CC
and a 3300 pF capacitor to
ground to obtain the nominal switching frequency of 26.5 kHz.
14
13
24
C
2
Comparator input channel 2. This input senses the instantaneous voltage across the
sensing resistor, filtered by an RC network. The threshold voltage for the comparator is
(0.450 / 2.5) V
R1
, i.e. 450 mV at V
R1
= 2.5 V.
15
14
25
V
R2
Reference voltage, channel 2. Controls the threshold voltage for the comparator and hence
the output current. Input resistance is typically 2.5 kohms,
20%.
16
15
26
CD
2
Current decay control, channel 2. A logic HIGH on this input results in
slow current decay,
a LOW results in
fast current decay, see "Functional Description."
17
16
27
Phase
2
Controls the direction of motor current at outputs M
A2
and M
B2
. Motor current flows from M
A2
to M
B2
when Phase
2
is HIGH.
20
19
4
M
A2
Motor output A, channel 2. Motor current flows from M
A2
to M
B2
when Phase
2
is HIGH.
21
20
5
V
MM2
Motor supply voltage, channel 2, 10 to 40 V. V
MM1
and V
MM2
should be connected together.
22
21
6
E
2
Common emitter, channel 2. This pin connects to a sensing resistor to ground.
23
22
7
M
B2
Motor output B, channel 2. Motor current flows from M
A2
to M
B2
when Phase
2
is HIGH.
1
2
3
4
5
6
8
9
10
11
22
21
20
19
18
17
16
15
14
13
12
GND
MA
1
CD
1
MA
2
GND
NC
Phase
1
PBL
3771/1 SO
MB
1
E
1
VMM
1
NC
MB
2
E
2
VMM
2
VR
1
VR
2
C
2
C
1
CD
2
V
cc
RC
23
24
GND
GND
Phase
2
7
PBL 3771/1
5
FAST Current Decay
SLOW Current Decay
Motor Current
Time
1
3
2
Figure 5. Output stage with current paths
during turn -on, turn-off and phase shift.
Figure 6. Typical stepper motor application with PBL 3771/1.
Functional Description
Each channel of the PBL 3771/1
consists of the following sections: an
H-bridge output stage, capable of driving
up to 650 mA continuous motor current
(or 500 mA, both channels driven), a
logic section that controls the output
transistors, an S-R flip-flop, and two
comparators. The oscillator is common
to both channels.
Constant current control is achieved
by switching the current to the windings.
This is done by sensing the (peak)
voltage across a current-sensing
resistor, R
S
, effectively connected in
series with the motor winding, and
feeding that voltage back to a
comparator. When the motor current
reaches a threshold level, determined by
the voltage at the reference input, V
R
,
the comparator resets the flip-flop, which
turns off the output transistors. The
current decreases until the clock
oscillator triggers the flip-flop, which
turns on the output transistors again,
and the cycle is repeated.
The current-decay rate during the
turn-off portion of the switching cycle,
can be selected fast or slow by the CD
input.
In slow current-decay mode, only one
of the lower transistors in the H-bridge
(those closest to the negative supply) is
switched on and off, while one of the
upper transistors is held constantly on.
During turn-off, the current recirculates
through the upper transistor (which one
depends on current direction) and the
corresponding free-wheeling diode
connected to V
MM
, see figure 5.
In fast current decay mode, both the
upper and lower transistors are
switched. During the off-time, the
freewheeling current is opposed by the
supply voltage, causing a rapid dis-
charge of energy in the winding.
Fast current decay may be required in
half- and microstepping applications
when rapid changes of motor current are
necessary. Slow current decay,
however, gives less current ripple, and
should always be selected, if possible, to
mini-mize core losses and switching
noise.
Applications Information
Current control
The output current to the motor winding
is mainly determined by the voltage at
the reference input and the value of the
sensing resistor, R
S
.
Chopping frequency, winding
inductance, and supply voltage will affect
the current level, but to much less
extent. Fast current decay setting will
produce somewhat lower (average)
current than slow current decay. The
peak current through the sensing
resistor (and motor winding) can be
expressed as:
I
M,peak
= 0.18 (V
R
/ R
S
)
[A]
i.e., with a recommended value of 1 ohm
for the sensing resistor, R
S
, a 2.5 V
reference voltage will produce an output
current of approximately 450 mA. To
improve noise immunity on the V
R
input,
the control range may be increased to
5 volts if R
S
is correspondingly changed
to 2 ohms.
3
2 1
R
s
7
8
9
16
15
14
Phase
CD
V
Phase
CD
V
1
1
2
2
R1
R2
E
C
E
C
GND
RC
PBL 3771/1
15 kW
3 300 pF
1.0 W
1.0 W
M
M
M
M
A1
B1
A2
B2
V
CC
V
V
MM1
MM2
+5 V
4
1
19
22
11
3
20
12
5, 6,
17, 18
2
13
21
10
1
1
2
2
R S
STEPPER
MOTOR
V
MM
Pin numbers refer
to DIL package.
GND (V
)
1 kW
1 kW
820 pF
820 pF
RS
0.1 mF
0.1 mF
+
10 mF
V (+5 V)
CC
GND
(V )
CC
MM
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